The present invention relates to a plasma processing apparatus, and in particular, to a plasma processing apparatus capable of reducing deposited substance fixed onto an objective item to be processed.
In a production process to produce a semiconductor device such as a Dynamic Random Access Memory (DRAM) and a microprocessor, there are widely employed a plasma etching apparatus and a plasma ashing (resist removing) apparatus which use weakly ionized plasma. With development of a technique to produce a semiconductor device in finer structure, thickness of the resist thin film becomes smaller. As a result of the reduction of the thickness, it is required in the etching that the resist consuming rate is lowered (the selective ratio is improved) and resist damage is suppressed. For this purpose, processing gas with a large deposition property capable of generating a large amount of deposited substance is often employed in many cases.
When such processing gas is employed, deposited substance is fixed onto a periphery of a rear surface of the objective item during the plasma processing. That is, in the etching apparatus, a mounting unit thereof to mount the objective item thereon has a diameter smaller than a diameter of the objective item. Therefore, the periphery of the rear surface of the objective item is exposed during the etching, and the deposited substance is fixed onto the exposed periphery of rear surface of the objective item.
When the deposited substance on the periphery of rear surface peels off from a wafer, for example, during transport thereof, the deposited substance contaminates as a foreign particle the semiconductor device production line, leading to yield reduction. Therefore, removal of the deposited substance is essential to the production line.
To remove the deposited substance on the periphery of the rear surface of the objective item or to prevent deposition of such substance, there have been known a method to supply reactive gas onto the periphery of the rear surface to remove the deposited substance (JP-A-2004-200353) and a method in which a cover is disposed over the periphery of the rear surface to conduct the etching with the cover to thereby prevent the deposited substance from fixing onto the periphery (JP-A-2004-200219).